Lateral strength of nailed timber connections with decay

Loading tests were conducted on nailed connections with decay due to a brown rot fungus. The effect of the decay on the lateral strength of nailed connections was investigated. After loading tests, the sound and decayed regions of a nailed connection were observed in the cross section, which was cut parallel to the grain through the nailed point. The nailed connections with decay showed a low load during initial deformation when the main and side members had a decayed region in the boundary between them. The nailed connections showed low load after yielding when the sound region in the main member decreased. The yield load of nailed connections with decay was calculated based on the yield theory. The model of calculations had sound and decay regions within a member. The yield load of nailed connections obtained by the calculation based on the yield theory agreed with the results obtained by experiments when significant decay in a direction parallel to the grain was observed in the main and side members. This result indicates that the yield theory can estimate the yield load of nailed connections not only with a sound member, but also a member that is partly or wholly decayed

Effect of decay on shear performance of dowel-type timber joints

Monotonic and reversed cyclic loading tests were conducted on dowel-type timber joints with varying degrees of wood decay due to Fomitopsis palustris (Berk. et Curt.), a brown rot fungus, and the effect of decay on various shear performances of dowel-type joints was investigated. For joints affected by the brown rot fungus, initial stiffness, yield load and maximum load of dowel-type joints were significantly decreased, even with a small mass loss of wood and reductions in shear performance were the largest for initial stiffness, followed by yield load and maximum load, in that order. For a 1% reduction of the yield load, initial stiffness and maximum load showed reductions of 1.15% and 0.77%, respectively. When dowel-type joints that had been exposed to the brown rot fungus were subjected to reversed cyclic loading, the gap between the dowel and the lead hole of the wood was increased and equivalent viscous damping was decreased. These results indicate that decay around the dowel lead hole especially affects the load-displacement behavior at small displacement level and dowel-type joints under cyclic loading have very low resistance to forces acting on wooden structure

Withdrawal strength of nailed joints with decay degradation of wood and nail corrosion

Nailed timber joints are widely used in timber structures, and their deterioration may cause significant damage. We investigated the withdrawal strength of joints using steel wire nails in specimens exposed to a brown-rot fungus. We also examined the effects of nail corrosion on withdrawal strength, because high humidity conditions accelerate not only wood decay but also the corrosion of nails. We found that nail corrosion increased the withdrawal strength. The ratios of withdrawal strength of nailed joints with rusted nails to that of joints with a minimally rusted nails were 1.47 and 1.56 in joints nailed in radial and tangential directions to annual rings, respectively. Withdrawal strength, excluding the effects of nail corrosion, had a negative correlation with mass loss and Pilodyn-pin-penetration-depth-ratio. We estimated the withdrawal strength of the nailed joint with decayed wood and rusted nails by multiplying the values from the empirical formula (obtained from mass loss and Pilodyn-pin-penetration-depth-ratio) by 1.47 and 1.56 for joints nailed in radial and tangential direction to annual rings, respectively

Nondestructive measurement of cross-sectional shape of a tree trunk

To evaluate windthrow resistance with respect to stem breakage, a nondestructive method for determining the shape of trunk cross sections was developed. In this method, the coordinates of multiple gauge points set on the perimeter of a trunk are calculated by measuring the distances between them. The shape between the gauge points is generated with the use of a profile gauge placed between them. Measurement tests were conducted using profile gauges with lengths of 300 and 900 mm on model specimens with four shape patterns and four different diameters. The accuracy of the estimation was verified by comparing the section modulus calculated for the generated image and for the photograph. The average ratio of section modulus (generated/photo) for all specimens was 0.994, which indicates that the proposed method is highly accurate. The section moduli of hollow trunks can be evaluated using the profile method together with the drill resistance technique on the condition that 26% of the trunk diameter could be drilled without skew

Bending resistance of repaired column members and shear resistance of opening frames with repaired columns of conventional Japanese wooden houses

In many cases of reparing Japanese conventional wooden houses, decayed lower parts of columns should be replaced with new wood material. Bending resistance of columns repaired by four methods and shear resistance of opening frames with those repaired columns were investigated in this study. Bending tests of the repaired columns showed differences in initial bending stiffness and maximum bending moment among the combinations of repair methods and loading directions. Racking tests were conducted on door opening frames with conventional door head member or upper partial walls sheathed with 12mm thick plywood. The conventional frame specimens broke at door head-column joints with no obvious bending deformation of the columns, it resulted in little difference in load-shear deformation curves among the repair methods. The columns of plywood-sheathed specimens, on the other hand, were bent clearly after when the nails at the plywood to wood frame joints started to be pulled off. The load-shear deformation curves of the plywood-sheathed specimens did not vary regardless of the repair methods in small shear deformations, but affected by the repair methods as shear deformation increased